It can be anything! An apex, subdomain, or even a URL.

Results forwebmail.crossbowsec.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2021-06-07T04:56:41.707	2021-06-07T03:56:41	2021-09-05T03:56:41	autodiscover.crossbowsec.com	webmail.crossbowsec.com	C=US, O=Let's Encrypt, CN=R3
2021-06-07T04:56:41.448	2021-06-07T03:56:41	2021-09-05T03:56:41	autodiscover.crossbowsec.com	webmail.crossbowsec.com	C=US, O=Let's Encrypt, CN=R3
2021-04-07T23:15:50.802	2021-04-07T22:15:50	2021-07-06T22:15:50	crossbowsec.com	webmail.crossbowsec.com	C=US, O=Let's Encrypt, CN=R3
2021-04-07T23:15:50.406	2021-04-07T22:15:50	2021-07-06T22:15:50	crossbowsec.com	webmail.crossbowsec.com	C=US, O=Let's Encrypt, CN=R3
2021-02-05T10:58:58.682	2021-02-05T09:58:58	2021-05-06T09:58:58	autodiscover.crossbowsec.com	webmail.crossbowsec.com	C=US, O=Let's Encrypt, CN=R3
2021-02-05T10:58:58.514	2021-02-05T09:58:58	2021-05-06T09:58:58	autodiscover.crossbowsec.com	webmail.crossbowsec.com	C=US, O=Let's Encrypt, CN=R3